1. Field of the Invention
The present invention relates to the structure of signal transmission cable, and in particular to a flexible circuit cable with at least two bundled wire groups.
2. The Related Arts
In various modern electronic devices, since the amount of data transmitted through signal lines is getting larger and larger, the number of signal lines used must be more and more and the frequency with which signals are transmitted must be higher and higher. Consequently, a differential mode of high frequency transmission is commonly adopted to reduce electromagnetic interference (EMI). For example, such a transmission technique is widely applied to USB or LVDS signals to reduce EMI. However, after the assembling of the signal transmission lines is completed, these signal transmission lines are often bundled for, on the one hand, positioning and, on the other hand, protection. The conventionally adopted signal transmission line bundling techniques generally wrap and bundle all the signal transmission lines together and the material used for wrapping is a piece of insulation tape or a conductive fabric for mechanically protecting the wires and improving durability of folding and electrically shielding the high frequency transmission wires against EMI. Although interference caused by the external environment is reduced, yet due to the signals that are carried and transmitted by the signal transmission lines being of different frequencies, there is electromagnetic interference induced between the signal transmission lines. Combining all the signal transmission lines within the sane bundle would lead to the problem of electromagnetic interference between the signal transmission lines.
A conventional flat cable is generally structured by arraying a number of conductor wires that are covered with an outer insulation layer in a line to form a cable. Such a cable is widely applied to various electrical appliances, electronic equipments, computer facilities, and communication devices for transmission of signals. Such a conventional cable works just fine when used between fixedly connected components. However, in an application where a hinge structure is included, it does not suit the needs for such an application. Most of the currently available electronic equipments or communication devices include a hinge structure. For example, in the structure of a currently widely used telecommunication hand set, a cover or a screen is coupled to a main body of the hand set by a hinge structure. To allow electrical signals to transmit from the main body of hand set to the cover or screen, cable bundling techniques are currently available for handling the problem that a conventional cable is incapable of extending through a hinge structure. However, the cable bundling techniques are applied in such a way that all the wires of a cable are bundled together, which is then put collectively through a hinge structure. Such techniques require a sufficiently large space in the hinge structure to allow all the wires of the cable to simultaneously extend a narrow hole defined in the hinge. Thus, severe constraints are imposed on the designs of hinge structures.
Further, to meet the needs in space and use, product designs are of such a trend of being compact and light-weighted and occupying just an amount of space that is as small as possible. However, the conventional techniques of cable bundling impose a number of constraints to the layout of circuit board. Since the signal transmission lines of a bundled cable are connected to signal contacts of a circuit such that the signal contacts must be set on the circuit boards in a mutually spaced manner and not on the same area, yet all the signal transmission lines are bundled together, all the signal transmission lines must be extended for a longer length. This increases the wire cost. Further, all the signal transmission lines are bundled together in a single bundle and thus a relatively large bundle is formed. This requires an extremely large amount of space on the circuit board, making it is not possible for an electronic product to meet the needs of being compact and light-weighted. Further, the spatial arrangement of the circuit board is also subjected to undesired constraints and cannot be effectively used, leading to undesired difficult of design.